Germany, France and Italy temporarily suspended the use of AstraZeneca’s COVID-19 vaccine Monday, joining a growing list of nations that paused use of the vaccine in recent days over concerns that it might be tied to blood clots.

Leading public health agencies, including the World Health Organization, say that millions of people have received the vaccine without experiencing blood clotting issues, and they caution that experts have not found a causative link between the vaccine and the conditions. The company has also defended the vaccine as safe, amid the flurry of suspensions.

The safety scare is a setback for AstraZeneca’s vaccine, which has already struggled with a perception that it is a less desirable shot because it had a lower overall efficacy rate in clinical trials than some others. There is, however, extensive data showing that the vaccine is safe and effective, and especially good at preventing severe illness and death. In many places across the world, it is the only shot available.

Public health experts expect medical conditions to turn up by chance in some people after they get any vaccine. In the vast majority of cases such illnesses have nothing to do with the shots.

Scientists also worry that suspensions could feed vaccine hesitancy at a time when some European countries are entering a third wave of the virus, and the world is in a race to inoculate as many people as possible, as dangerous virus variants proliferate.

The European Medicines Agency, the WHO and other regulators are investigating whether there is evidence of any link between the vaccine and blood clots.

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On Monday, the EMA reiterated its position that the benefit of the AstraZeneca vaccine outweighs the risk posed by possible side effects. And officials with the WHO emphasized that the regulators’ investigations are precautionary and cover the batches of vaccines produced in Europe — not the ones made in South Korean and Indian facilities.

“While we need to continue to be very closely monitoring this, we do not want people to panic,” Dr. Soumya Swaminathan, chief scientist at the WHO, said Monday. For the time being, she said, the WHO advises countries to continue vaccinating citizens with the AstraZeneca vaccine.

Tedros Adhanom Ghebreyesus, the director-general of the WHO, added that reviews of vaccine side effects are not unusual.

“It’s routine practice to investigate them, and it shows that the surveillance system works and that effective controls are in place,” he said Monday.

AstraZeneca defended its product on Sunday, saying that the company is continually monitoring its safety.

“Around 17 million people in the EU and U.K. have now received our vaccine, and the number of cases of blood clots reported in this group is lower than the hundreds of cases that would be expected among the general population,” said Ann Taylor, the company’s chief medical officer.

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In France, President Emmanuel Macron said Monday that the country would stop using the vaccine pending an assessment by the European Medicines Agency on its use.

“The decision that was taken, in accordance with our European policy, is to suspend AstraZeneca vaccinations as a precaution, with the hope of quickly picking them up again if the European Medicines Agency permits it,” Macron said at a news conference in southwestern France. “We have a simple guide, to follow the science and the competent health authorities, and to do so in the framework of a European strategy.”

In Italy, the decision was also “precautionary and temporary,” the Italian Medicines Agency said in a statement, adding that it, too, was waiting for more from the EMA.

In Germany, the Health minister, Jens Spahn, said the country’s decision to temporarily suspend administration of the AstraZeneca vaccine was “purely precautionary.” The decision came after the national health regulator decided that further studies of AstraZeneca were needed after cases of a “rare cerebral vein thrombosis” had occurred in seven recipients, the minister said. More than 1.6 million doses of AstraZeneca have been administered in Germany, which has relied heavily on the BioNTech-Pfizer vaccine.

Indonesia and the Netherlands also suspended the use of AstraZeneca’s vaccine, citing reports of unusual blood clotting problems among a few people who recently received the shots in Norway. Blood clots, particularly if they are large, can damage tissue or organs like the lungs, heart or brain. Severe cases can be fatal, but people with small clots can often be treated outside a hospital with prescription drugs.

Over the weekend, Norway said that four people who received a dose of the AstraZeneca vaccine had experienced blood clotting issues and all had low platelet counts. The country has reported two deaths in health care workers who each had an intracerebral hemorrhage. While Norway has paused the use of the vaccine, health officials have emphasized that they were acting out of caution and that there was no evidence the problems had been caused by the vaccine.

By contrast, Thailand said that it would resume issuing the AstraZeneca vaccine Tuesday, with Prime Minister Prayuth Chan-ocha among the first to receive it.

Denmark, Iceland and Congo are among the countries that have suspended use of the AstraZeneca vaccine.